1. Field of the Invention
The present invention relates to curable resinous compositions and more particularly relates to curable resinous coating compositions in which the resinous binder cures via a Michael addition reaction.
2. Brief Description of the Prior Art
Resinous coating compositions which cure via a Michael addition reaction are known in the art. Thus, for example, U.S. Pat. No. 3,975,251 to McGinniss discloses cationic electrodepositable compositions comprising an acid-solubilized polyamine resin in combination with polyacrylate curing agents. Upon electrodeposition, the polyamine resin deprotonates exposing primary or secondary amine groups which react via a Michael addition with the polyacrylate to form a cured coating on the cathode.
In such compositions, it is necessary that the polyamine resins be completely neutralized (100 percent or more of the total theoretical neutralization) in order to prevent any premature reaction between an unprotonated polyamine resin and the polyacrylate curing agent in the electrodeposition bath.
The present invention is an improvement over the compositions of U.S. Pat. No. 3,975,251. In the present invention, the alpha, beta-ethylenically unsaturated moieties in conjugatiion with carbonyl moieties are reacted with a primary and/or secondary amine which is volatile under curing conditions. Thus, any premature reaction before cure of the alpha, beta-ethylenically unsaturated moieties in conjugation with carbonyl moieties is avoided. When the compositions are heated to curing temperatures, it is believed the adduct decomposes releasing amine which volatilizes generating alpha, beta-ethylenically unsaturated carbonyls which cure via a Michael addition reaction with non-volatile primary and/or secondary amines present in the composition.